1. Field of the Invention
The present invention relates to a magnetoresistive element and relates to a magnetic device such as a magnetic head and a magnetic memory and a magnetic recording apparatus using the same.
2. Related Background Art
In recent years, developments have been carried out vigorously for applying a magnetoresistive effect to a magnetic head, a magnetic memory (Magnetic Random Access Memory (MRAM)) and the like. The MR effect is based on a conductive phenomenon depending on the spin of the electron, in which a resistance value of a multilayer film including a “magnetic layer/non-magnetic layer/magnetic layer” configuration varies with a relative angle between the magnetic orientations of the magnetic layers arranged adjacent to each other with the non-magnetic layer interposed therebetween. In general, when the magnetic orientations are parallel with each other, the resistance value becomes the minimum. Conversely, when the magnetic orientations are anti-parallel to each other, the resistance value becomes the maximum. Elements exploiting such a MR effect are referred to as MR elements. Among MR elements, elements with a non-magnetic layer made of a conductive material such as Cu are referred to as GMR elements, while elements with a non-magnetic layer made of an insulating material such as Al2O3 are referred to as TMR elements. In the TMR elements, a magnetoresistance change ratio (MR ratio) increases with increasing a spin polarization rate of magnetic layers sandwiching a non-magnetic layer. Currently, this TMR element is expected to be a MR element exerting a large MR ratio.
In order to apply this TMR element to a device such as a magnetic head or a MRAM, there is a need to further enhance and stabilize the output of the element. In addition, the element is required to have thermal stability capable of resisting the manufacturing process of the device. For instance, in the process for manufacturing a magnetic head, heat is applied generally at about 250° C. to 300° C. When the element is mounted in a hard disk drive (HDD), it is required to operate with stability at the operational environmental temperatures (e.g., around 150° C.) for a long time. Furthermore, while studies have been made to produce a MR element on a CMOS for the application as a MRAM device, the process for manufacturing the CMOS requires heat treatment at much higher temperatures (e.g., 400° C. to 450° C.).
However, when the conventional TMR element having a tunnel junction structure between a tunnel insulation layer and a magnetic layer undergoes the heat treatment at 300° or higher, the magnetoresistance properties (MR properties) deteriorate. Particularly, there is a tendency to degrade a MR ratio representing the output of the element. Thus, in order to apply the TMR element to a device such as a magnetic head and a MRAM, it becomes important to develop a TMR element whose MR properties have thermal stability in an increase in temperature of the element caused by the heat treatment and the like.